Polyamide resins possess excellent mechanical properties, moldability, and chemical resistance and have therefore been used in automotive parts, electric/electronic components, mechanical components, and many other applications. Articles made from polyamide resins can possess extremely desirable physical properties. However, in certain applications, it is desirable that polyamide resin compositions be flame retardant and meet the UL-94 standard for a high degree of flame retardance. This need has promoted research into a variety of methods for imparting flame retardance to polyamide resins. A common method of imparting flame retardance to thermoplastic resin compositions involves incorporating a halogenated organic compound such as brominated polystyrene as a flame retardant along with an antimony compound that acts as a synergist for the flame retardant. However, the use of halogenated flame retardants has certain drawbacks in that these materials tend to decompose or degrade at the temperatures used to mold polyamide compositions. The degradation products can corrode the barrels of compounding extruders, the surfaces of molding machines, and other melt processing equipment halogenated flame retardants come in contact with at elevated temperatures. This problem can be particularly pronounced in the case of semiaromatic polyamide compositions, as these materials often have melting points that are significantly higher than those of many aliphatic polyamides. The degradation products of halogenated flame retardants can also result in molded articles that have poor surface appearance.
It would thus be desirable to obtain a non-halogenated flame retardant semiaromatic polyamide composition that leads to reduced levels of corrosion of melt processing equipment while satisfying certain regulatory requirements.
The use of non-halogenated flame retardants such as phosphate or phosphinate compounds with triazine derivatives has been disclosed in WO 96/09344. U.S. Pat. No. 5,773,556 disclose compositions comprising polyamide and phosphinate or diphosphinate. U.S. Pat. No. 6,255,371 discloses compositions comprising polymers such as polyamide or polyester, with a flame retardant comprising phosphinate or diphosphinate and melamine derivatives such as condensation products of melamine.
More recently the down sizing trend of electrical & electronics devises requires a high melt flow increasingly for the use of flame retardant polyamide composition in the SMT applications. The use of the phosphinates can eliminate use of halogen containing material from the composition, however, it can decrease melt flow of the composition when the phosphinates dispersed in the polyamide matrix are not fully molten at a molding process.
U.S. patent application publication 2006/0030693 discloses the use of terephthalic acid as an agent to increase melt flow of a high temperature polyamide composition. However, it has been discovered that the use of terephthalic acid disclosed in this publication can lead to void formations during the SMT process.
There is a need for a high temperature flame retarded semiaromatic polyamide which does not cause, at relatively higher temperatures, the formation of voids and the deformation of plastic parts molded therefrom, while maintaining high melt flow (or low melt viscosity, as these terms are used interchangeably) in the molding process.